Cell-cell interactions in synovitis: antigen presenting cells and T cell interaction in rheumatoid arthritis

The synovial tissue in rheumatoid arthritis (RA) patients is enriched with mature antigen presenting cells (APCs) and many T lymphocytes. Interactions between APCs and T cells are essential for the initiation and amplification of T-cell-dependent immune responses, and may therefore play an important role in the chronic inflammatory processes in the synovium. The nature of the antigen(s) involved in RA still remains elusive. However, interactions and signaling through the costimulatory molecules CD28-CD80/86 and CD40-CD40L are critical during APC-T cell interaction for optimal cell activation. This review discusses how such costimulatory signals can be involved in the initiation and amplification of the inflammatory reactions in the synovium. Blocking of the signaling pathways involved in APC-T cell interactions might provide a specific immuno-therapeutic approach for the treatment of RA.     

Cell-cell interactions in synovitis: Antigen presenting cells and T cell interaction in rheumatoid arthritis

The synovial tissue in rheumatoid arthritis (RA) patients is enriched with mature antigen presenting cells (APCs) and many T lymphocytes. Interactions between APCs and T cells are essential for the initiation and amplification of T-cell-dependent immune responses, and may therefore play an important role in the chronic inflammatory processes in the synovium. The nature of the antigen(s) involved in RA still remains elusive. However, interactions and signaling through the costimulatory molecules CD28-CD80/86 and CD40-CD40L are critical during APC–T cell interaction for optimal cell activation. This review discusses how such costimulatory signals can be involved in the initiation and amplification of the inflammatory reactions in the synovium. Blocking of the signaling pathways involved in APC–T cell interactions might provide a specific immuno-therapeutic approach for the treatment of RA.     

Mast cells enhance T cell activation: importance of mast cell costimulatory molecules and secreted TNF

We recently reported that mast cells stimulated via FcepsilonRI aggregation can enhance T cell activation by a TNF-dependent mechanism. However, the molecular mechanisms responsible for such IgE-, Ag- (Ag-), and mast cell-dependent enhancement of T cell activation remain unknown. In this study we showed that mouse bone marrow-derived cultured mast cells express various costimulatory molecules, including members of the B7 family (ICOS ligand (ICOSL), PD-L1, and PD-L2) and the TNF/TNFR families (OX40 ligand (OX40L), CD153, Fas, 4-1BB, and glucocorticoid-induced TNFR). ICOSL, PD-L1, PD-L2, and OX40L also are expressed on APCs such as dendritic cells and can modulate T cell function. We found that IgE- and Ag-dependent mast cell enhancement of T cell activation required secreted TNF; that TNF can increase the surface expression of OX40, ICOS, PD-1, and other costimulatory molecules on CD3(+) T cells; and that a neutralizing Ab to OX40L, but not neutralizing Abs to ICOSL or PD-L1, significantly reduced IgE/Ag-dependent mast cell-mediated enhancement of T cell activation. These results indicate that the secretion of soluble TNF and direct cell-cell interactions between mast cell OX40L and T cell OX40 contribute to the ability of IgE- and Ag-stimulated mouse mast cells to enhance T cell activation.     

Pertussis toxin-induced cytokine differentiation and clonal expansion of T cells is mediated predominantly via costimulation

Pertussis toxin (PTX) has potent immunologic adjuvant activity in vivo and concomitantly enhances both T helper type (Th1) and Th2 cytokine responses. The PTX-induced enhancement of Th1 and Th2 immunity is mediated via the activation of antigen presenting cells (APCs), but the underlying mechanism is not known. Here we asked whether the adjuvant activity of PTX on T cell immunity was mediated by cytokines and/or costimulatory signals. The results show that in vivo blockade of CD28-CD80/86 costimulation essentially abrogated PTX-mediated enhancement of antigen-specific Th1 and Th2 responses. Blockade of CD40L-CD40 interactions was less efficient in inhibiting PTX-mediated enhancement of Th1 and Th2 responses. In contrast, the adjuvant activity of PTX was not mediated via cytokines, because neither Th1 nor Th2 responses were substantially impaired in mice deficient for IL-12, IFN-gamma, IL-4, IL-5, or IL-6. Collectively, the data suggest that PTX mediates its adjuvant effects on T cell cytokine differentiation and clonal expansion via the modulation of costimulatory molecules on APCs. Understanding the costimulatory pathways targeted by PTX could lead to the design of novel adjuvants that selectively induce Th1 or Th2 immunity.     

Characterization of cytokine, growth factor receptor, costimulatory and adhesion molecule expression patterns of bone marrow blasts in relapsed childhood B cell precursor all

Relapse of childhood acute lymphoblastic leukaemia (ALL) comprises a leading challenge of investigation. Characterization of leukaemic cells regarding their potency to express growth factors and surface molecules can provide insight into their aberrant biology. Thus, we analyzed bone marrow blasts from 10 children with relapsed B cell precursor ALL. The gene and protein expression of essential haematopoietic growth factors (IL-2, IL-4, IL-7, IL-10, IL-15, IFN-gamma, G-CSFR), their corresponding receptors as well as the expression pattern of adhesion molecules (ICAM-1, CD58) and costimulatory proteins (CD40, CD40L, B7.1, B7.2, CD28, MHC-I and II) was analyzed by RT-PCR and flow cytometry. Constitutive gene expression was found for IL-7, IL-10, IL-15 and IFN-gamma and their corresponding receptors. Flow-cytometric analysis showed that IL-10R, IL-7Ralpha, IL-4Ralpha and the gamma(c)chain are constitutively expressed, and that some cells bear the G-CSFR. IL-10 and IL-15 protein-producing leukaemic cells were easily detectable. The neoplastic cells mainly lack B7.1, and ICAM-1 is mostly decreased. Furthermore, high CD40, and, surprisingly, CD40L expression could be found. These studies show that ALL cells are likely to be sensitive to many growth factors and some factors are produced by the neoplastic cell itself. The secretion of IL-10 by leukaemic cells, and the absence or downregulation of conventional adhesion and costimulatory molecules might represent an effective mechanism of escape of immune surveillance in relapsed ALL.     

Potent costimulation of human CD8 T cells by anti-4-1BB and anti-CD28 on synthetic artificial antigen presenting cells

The in vitro generation of cytotoxic T lymphocytes (CTLs) for anticancer immunotherapy is a promising approach to take patient-specific therapy from the bench to the bedside. Two criteria must be met by protocols for the expansion of CTLs: high yield of functional cells and suitability for good manufacturing practice (GMP). The antigen presenting cells (APCs) used to expand the CTLs are the key to achieving both targets but they pose a challenge: Unspecific stimulation is not feasible because only memory T cells are expanded and not rare naïve CTL precursors; in addition, antigen-specific stimulation by cell-based APCs is cumbersome and problematic in a clinical setting. However, synthetic artificial APCs which can be loaded reproducibly with MHC-peptide monomers and antibodies specific for costimulatory molecules could resolve these problems. The purpose of this study was to investigate the potential of complex synthetic artificial APCs in triggering the costimulatory molecules CD28 and 4-1BB on the T cell. Anti-4-1BB antibodies were added to an established system of microbeads coated with MHC-peptide monomers and anti-CD28. Triggering via CD28 and 4-1BB resulted in strong costimulatory synergy. The quantitative ratio between these signals determined the outcome of the stimulation with optimal results when anti-4-1BB and anti-CD28 were applied in a 3:1 ratio. Functional CTLs of an effector memory subtype (CD45RA^? CCR7^?) were generated in high numbers. We present a highly defined APC platform using off-the-shelf reagents for the convenient generation of large numbers of antigen-specific CTLs.     

Therapeutic peptidomimetic strategies for autoimmune diseases: costimulation blockade.

Cognate interactions between immune effector cells and antigen-presenting cells (APCs) govern immune responses. Specific signals occur between the T-cell receptor peptide and APCs and nonspecific signals between pairs of costimulatory molecules. Costimulation signals are required for full T-cell activation and are assumed to regulate T-cell responses as well as other aspects of the immune system. As new discoveries are made, it is becoming clear how important these costimulation interactions are for immune responses. Costimulation requirements for T-cell regulation have been extensively studied as a way to control many autoimmune diseases and downregulate inflammatory reactions. The CD28:B7 and the CD40:CD40L families of molecules are considered to be critical costimulatory molecules and have been studied extensively. Blocking the interaction between these molecules results in a state of immune unresponsiveness termed 'anergy'. Several different strategies for blockade of these interactions are explored including monoclonal antibodies (mAbs), Fab fragments, chimeric, and/or fusion proteins. We developed novel, immune-specific approaches that interfere with these interactions. Using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis mediated by central nervous system (CNS)-specific T-cells, we developed a multi-targeted approach that utilizes peptides for blockade of costimulatory molecules. We designed blocking peptide mimics that retain the functional binding area of the parent protein while reducing the overall size and are thus capable of blocking signal transduction. In this paper, we review the role of costimulatory molecules in autoimmune diseases, two of the most well-studied costimulatory pathways (CD28/CTLA-4:B7 and CD40:CD40L), and the advantages of peptidomimetic approaches. We present data showing the ability of peptide mimics of costimulatory molecules to suppress autoimmune disease and propose a mechanism for disease suppression.     

Cutting edge: The transmembrane E3 ligase GRAIL ubiquitinates the costimulatory molecule CD40 ligand during the induction of T cell anergy

Activation of naive T lymphocytes is regulated through a series of discrete checkpoints that maintain unresponsiveness to self. During this multistep process, costimulatory interactions act as inducible signals that allow APCs to selectively mobilize T cells against foreign Ags. In this study, we provide evidence that the anergy-associated E3 ubiquitin ligase GRAIL (gene related to anergy in lymphocytes) regulates expression of the costimulatory molecule CD40L on CD4 T cells. Using its luminal protease-associated domain, GRAIL binds to the luminal/extracellular portion of CD40L and facilitates transfer of ubiquitin molecules from the intracellular GRAIL RING (really interesting new gene) finger to the small cytosolic portion of CD40L. Down-regulation of CD40L occurred following ectopic expression of GRAIL in naive T cells from CD40(-/-) mice, and expression of GRAIL in bone marrow chimeric mice was associated with diminished lymphoid follicle formation. These data provide a model for intrinsic T cell regulation of costimulatory molecules and a molecular framework for the initiation of clonal T cell anergy.     

The effect of LIGHT in inducing maturation of monocyte-derived dendritic cells from MDS patients

LIGHT is a recently cloned novel cytokine belonging to the TNF family that is selectively expressed on immature dendritic cells (iDCs) generated from monocytes isolated from human PBMCs. In these studies, we demonstrate that exogenous soluble LIGHT or soluble CD40 ligand (CD40L) can promote monocyte-derived dendritic cell maturation in vitro by the up-regulation of CD86, CD80, CD83, and HLA-DR antigen expression. Immature dendritic cells differentiated from monocytes of MDS patients displayed lower levels of costimulatory and HLA-DR molecules compared with iDCs differentiated from monocytes of normal subjects. However, upon induction of maturation by LIGHT or CD40L, the expression of costimulatory and HLA-DR molecules is comparable between DCs from MDS and normal subjects. Exogenous LIGHT- and CD40L-stimulated mature DCs (mDCs) also displayed increased antigen presentation to autologous T lymphocytes (tetanus toxin) or allogeneic T lymphocytes in mixed lymphocyte reactions. DCs matured by LIGHT showed increased secretion of IL-6, IL-12p75, and TNF-, but not IL-1. We conclude that both LIGHT and CD40L are immunoregulating factors that induce monocyte-derived iDCs from MDS patients to undergo maturation resulting in increased antigen presentation and T-cell activation. Monocyte-derived DCs can be stimulated to undergo phenotypic and functional changes with LIGHT that might be applied in the development of a DC-based vaccine for MDS treatment.     

Not all effector CD8+ T cells are alike

As naive CD8+ T cells circulate throughout the bloodstream and secondary lymphoid tissues (i.e. spleen and lymph nodes), they sample complexes of peptides and MHC class I molecules expressed on the surface of professional antigen presenting cells (APCs). A proper fit between lymphocyte and APCs sets into motion a complex series of events that result in the generation of activated cytotoxic T lymphocytes (CTLs) that are the principal immune effectors against infected and transformed cells. Owing to the severe immunopathology that can result from the aberrant stimulation of CTLs, the activation of na?ve CD8(+) T cells is a tightly regulated process. A growing body of evidence suggests that the quality of stimulation na?ve CD8+ T cells receive during the induction and maintenance of an immune response dictates the functional competency of the responding antigen-specific CTLs, and that CD8+ T cells and their progeny "effector cells" can exist long-term in vastly different activation states.     

Control of NKT cell differentiation by tissue-specific microenvironments

CD1d-restricted Valpha14 NKT cells play an important role in both Th1- and Th2-type immune responses. To determine whether NKT cells develop two functionally distinct subsets that provoke different types of responses, we examined the phenotypes and cellular functions of NK1.1(+) and DX5(+) T cells. We found that both NK1.1(+) and DX5(+) T cells are CD1d-restricted Valpha14 T cells with identical Ag specificities, phenotypes, tissue locations, and functions. Similar to the NK1.1 marker, the DX5 marker (CD49b) is expressed on mature NKT cells in both NK1.1 allele-positive and allele-negative strains. However, when NK1.1(+) and DX5(+) NKT cells isolated from different tissues were compared, we found that thymic and splenic NKT cells differed not only in their cytokine profiles, but also in their phenotype and requirements for costimulatory signals. Thymic NKT cells displayed the phenotype of activated T cells and could be fully activated by TCR ligation. In contrast, splenic NKT cells displayed the phenotype of memory T cells and required a costimulatory signal for activation. Furthermore, the function and phenotype of thymic and splenic NKT cells were modulated by APCs from various tissues that expressed different levels of costimulatory molecules. Modulation of NKT cell function and differentiation may be mediated by synergic effects of costimulatory molecules on the surface of APCs. The results of the present study suggest that the costimulatory signals of tissue-specific APCs are key factors for NKT cell differentiation, and these signals cannot be replaced by anti-CD28 or anti-CD40 ligand Abs.     

Human acute lymphoblastic leukemia (ALL) blasts as accessory cells during T-cell activation: differences between patients in costimulatory capacity affect proliferative responsiveness and cytokine release by activated T cells

The ability of acute lymphoblastic leukemia (ALL) blasts to mediate costimulatory signals during T-lymphocyte activation was investigated in an experimental model in which monoclonal T-cell populations were stimulated with standardized activation signals (anti-CD3 and anti-CD28 monoclonal antibodies; phytohemagglutinin, PHA). Leukemia cells from 12 consecutive ALL patients with high peripheral blood blast counts were studied. Proliferative T-cell responses were detected for a majority of these patients when irradiated leukemia blasts were used as accessory cells during activation. T-cell cytokine release was also observed for most patients when using nonirradiated ALL accessory cells. Low or undetectable cytokine levels were usually observed for CD8+ clones, whereas the CD4+ clones often showed a broad cytokine response with release of interleukin-2 (IL-2), IL-4, IL-10, IL-13 and interferon gamma(IFN-gamma) in the presence of the ALL accessory cells. ALL blasts were also able to function as allostimulatory cells for normal peripheral blood mononuclear responder cells. However, both T-cell proliferation and cytokine release showed a wide variation between ALL patients. The accessory cell function of ALL blasts showed no correlation with the release of immunomodulatory mediators (IL-2, IL-10, IL-15) or the expression of any single adhesion/costimulatory membrane molecule (CD54, CD58, CD80, CD86) by the blasts. We conclude that for a majority of patients, native ALL blasts can mediate costimulatory signals needed for accessory cell-dependent T-cell activation, but differences in costimulatory capacity between ALL patients affects both the proliferative responsiveness and cytokine release by activated T cells.     

CD40L and IL-4 stimulation of acute lymphoblastic leukemia cells results in upregulation of mRNA level of FLICE--an important component of apoptosis

The use of cancer vaccines based on dendritic cells (DC) presenting tumor antigens can be a promising tool in the treatment of leukemia. The functional characteristics of leukemia derived DC is still to be elucidated. CD40 promotes survival, proliferation and differentiation of normal B cells. CD40 triggering was used to enhance the poor antigen-presenting capacity of leukemic B-cells. Since it is still unclear whether CD40 ligation drives neoplastic B-cells to apoptosis or not, we assessed the mRNA expression of FLICE, FAS, FADD and TRADD - important components of apoptosis machinery, using real-time PCR in acute lymphoblastic leukemia cells before and after CD40 and IL-4 stimulation. ALL cells stimulated with CD40L/IL-4 expressed dendritic cell phenotype at mRNA and protein levels (upregulation of main costimulatory and adhesion molecules noted in real-time RT PCR and flow cytometry); they also expressed higher amounts of mRNA for FLICE, TRADD and FADD after CD40L/IL-4 stimulation. However differences statistically significant comparing cells cultured with CD40L/IL-4 and medium alone regarded only FLICE. Concluding, we showed upregulation of important elements of apoptosis at mRNA level in ALL cells after CD40 ligation.     

Bi-directional activation between human airway smooth muscle cells and T lymphocytes: role in induction of altered airway responsiveness

Because both T lymphocyte and airway smooth muscle (ASM) cell activation are events fundamentally implicated in the pathobiology of asthma, this study tested the hypothesis that cooperative intercellular signaling between activated T cells and ASM cells mediates proasthmatic changes in ASM responsiveness. Contrasting the lack of effect of resting human T cells, anti-CD3-activated T cells were found to adhere to the surface of naive human ASM cells, increase ASM CD25 cell surface expression, and induce increased constrictor responsiveness to acetylcholine and impaired relaxation responsiveness to isoproterenol in isolated rabbit ASM tissues. Comparably, exposure of resting T cells to ASM cells prestimulated with IgE immune complexes reciprocally elicited T cell adhesion to ASM cells and up-regulated T cell expression of CD25. Extended studies demonstrated that: 1) ASM cells express mRNAs and proteins for the cell adhesion molecules (CAMs)/costimulatory molecules, CD40, CD40L, CD80, CD86, ICAM-1 (CD54), and LFA-1 (CD11a/CD18); 2) apart from LFA-1, ASM cell surface expression of the latter molecules is up-regulated in the presence of activated T cells; and 3) pretreatment of ASM cells and tissues with mAbs directed either against CD11a or the combination of CD40 and CD86 completely abrogated both the activated T cell-induced changes in expression of the above CAMs/costimulatory molecules in ASM cells and altered ASM tissue responsiveness. Collectively, these observations identify the presence of bi-directional cross-talk between activated T cells and ASM cells that involves coligation of specific CAMs/costimulatory molecules, and this cooperative intercellular signaling mediates the induction of proasthmatic-like changes in ASM responsiveness.     

M2 macrophages induced by prostaglandin E2 and IL-6 from cervical carcinoma are switched to activated M1 macrophages by CD4+ Th1 cells

Monocytes attracted by tumor-induced chronic inflammation differentiate to APCs, the type of which depends on cues in the local tumor milieu. In this work, we studied the influence of human cervical cancer cells on monocyte differentiation and showed that the majority of cancer cells either hampered monocyte to dendritic cell differentiation or skewed their differentiation toward M2-like macrophages. Blocking studies revealed that M2 differentiation was caused by tumor-produced PGE(2) and IL-6. TGF-β, IL-10, VEGF, and macrophage colony-stimulating factor did not play a role. Notably, these CD14(+)CD163(+) M2 macrophages were also detected in situ. Activation of cancer cell-induced M2-like macrophages by several TLR-agonists revealed that compared with dendritic cells, these M2 macrophages displayed a tolerogenic phenotype reflected by a lower expression of costimulatory molecules, an altered balance in IL-12p70 and IL-10 production, and a poor capacity to stimulate T cell proliferation and IFN-γ production. Notably, upon cognate interaction with Th1 cells, these tumor-induced M2 macrophages could be switched to activated M1-like macrophages that expressed high levels of costimulatory molecules, produced high amounts of IL-12 and low amounts of IL-10, and acquired the lymphoid homing marker CCR7. The effects of the interaction between M2 macrophages and Th1 cells could partially be mimicked by activation of these APCs via CD40 in the presence of IFN-γ. Our data on the presence, induction, and plasticity of tumor-induced tolerogenic APCs in cervical cancer suggest that tumor-infiltrated Th1 cells can stimulate a tumor-rejecting environment by switching M2 macrophages to classical proinflammatory M1 macrophages.     

Acquisition of CD80 (B7-1) by T cells

Activation of T cells usually requires two signals. Signal 1 is mediated via a peptide-MHC on the APC; signal 2 is mediated via a costimulatory molecule on the APC surface. We demonstrate here that naive CD4(+) T cells actually acquire the costimulatory molecule CD80 (B7-1) from syngeneic APCs after activation. This phenomenon was demonstrated showing acquisition of CD80 by T cells from CD80/CD86 (B7-2) knockout mice, and by treating T cells with cyclohexamide to further rule out endogenous expression of CD80 by T cells. Moreover, no CD80 mRNA could be detected in T cells that had acquired CD80. The amount of acquisition of CD80 by T cells was shown to be directly related to both the strength of signal 1 and the amount of CD80 on the APC. Specificity of this acquisition was also shown by the lack of acquisition by T cells from CD28 knockout mice (implicating CD28 in this process), the lack of acquisition of CD40 (another molecule on the APC surface) by T cells, and confocal microscopy studies. We demonstrate for the first time that 1) naive T cells, following acquisition of CD80 from APCs, were themselves shown to be capable of acting as APCs; and 2) memory T cells that have acquired CD80 from APCs undergo apoptosis in the presence of increased levels of signal 1. Thus we demonstrate both immunostimulatory and immunoregulatory functions as a result of CD80 acquisition by different T cell populations.     

Transfer of T cell surface molecules to dendritic cells upon CD4+ T cell priming involves two distinct mechanisms

Activation of CD4(+) T cells by APCs occurs by multiple Ag recognition events including the exchange of costimulatory signals and cytokines. Additionally, the T cells acquire APC-derived surface molecules. Herein, we describe for the first time the transfer of human and murine T cell surface receptors to APCs after Ag-specific interaction. This transfer occurs in two qualitatively different phases. The first group of molecules (e.g., CD2) derived from the T cell surface was transferred rapidly after 2 h of interaction, was strongly bound on the DC surface (acid wash-resistant), was strictly dependent on dendritic cell-T cell contact, and transferred independently of T cell activation. The second group, including the CD3/TCR complex, CD27, and OX40, was of intracellular origin, transferred later after 10-16 h in a cell-cell contact-independent fashion, was noncovalently bound, and was strictly dependent on Ag-specific T cell activation. Functionally, murine dendritic cells that received TCR molecules from OVA-specific CD4(+) T cells after Ag-specific interaction were less efficient in priming naive CD4(+) T cells of the same specificity without losing their ability for CD8(+) T cell stimulation, indicating that the transferred TCR molecules mask the Ag-bearing MHC II molecules, thereby reducing their accessibility to following Ag-specific CD4(+) T cells. While the first group of transferred T cell surface molecules might facilitate the detachment of the CD4(+) T cell from the dendritic cell during the early scanning phases, the second group could play an important immunomodulatory role in intraclonal competition of T cells for APC access, making the physical presence of CD4(+) T cells unnecessary.     

A recombinant vector expressing transgenes for four T-cell costimulatory molecules (OX40L,B7-1, ICAM-1, LFA-3) induces sustained CD4+ and CD8+ T-cell activation,protection from apoptosis,and enhanced cytokine production

The role of OX40L on the activation of T cells was investigated using poxvirus vectors expressing OX40L alone or in combination with three other T-cell costimulatory molecules: B7-1, ICAM-1, and LFA-3. Poxvirus vector-infected cells were used to stimulate nai;ve or activated CD4(+) and CD8(+) T cells. These studies demonstrate that (a) OX40L plays a role in sustaining the long-term proliferation of CD8(+) T cells in addition to the known effect on CD4(+) T cells following activation, (b) OX40L enhances the production of Th1 cytokines (IL-2, IFN-gamma, and TNF-alpha) from both CD4(+) and CD8(+) while no change in IL-4 expression was observed, and (c) the anti-apoptotic effect of OX40L on T cells is likely the result of sustained expression of anti-apoptotic genes while genes involved in apoptosis are inhibited. In addition, these are the first studies to demonstrate that the combined use of a vector driving the expression of OX40L with three other costimulatory molecules (B7-1, ICAM-1, and LFA-3) both enhances initial activation and then further potentiates sustained activation of nai;ve and effector T cells.     

Chronic lymphocytic leukemia (CLL) cells genetically modified to express B7-1, ICAM-1, and LFA-3 confer APC capacity to T cells from CLL patients

In chronic lymphocytic leukemia (CLL), malignant B cells and nonmalignant T cells exhibit dysfunction. We previously demonstrated that infection of CLL cells with modified vaccinia Ankara (MVA) expressing the costimulatory molecules B7-1, ICAM-1, and LFA-3 (designated TRICOM) increased expression of these costimulatory molecules on the surface of CLL cells and thus augmented their antigen-presenting capability. Here, we evaluate the effect of MVA-TRICOM-modified CLL cells on T cells. Following incubation with irradiated MVA-TRICOM-modified CLL cells, allogeneic and autologous CD4⁺ and CD8⁺ T cells expressed significantly higher levels of B7-1, ICAM-1, and LFA-3. We show that this increase was the result of physical acquisition from the antigen-presenting cells (APCs), and that purified T cells that acquired costimulatory molecules from MVA-TRICOM-modified CLL cells were able to stimulate the proliferation of untreated T cells. These results demonstrate for the first time that T cells from CLL patients can acquire multiple costimulatory molecules from autologous CLL cells and can then act as APCs themselves. Given the immunodeficiencies characteristic of CLL, enhancing the antigen-presenting function of CLL cells and T cells simultaneously could be a distinct advantage in the effort to elicit antitumor immune responses. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.